A mud fortress on top of Busosan, it was the primary Baekje defense against the Shilla for 123 years, starting in 538, during the 16th year of King Seong's reign. It was reconstructed in 605, the sixth year of King Muwang, and it's remained untouched to this day. Historians believe that the Baekje royalty used the fortress as a park during times of peace.